Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface showing my new design.

The dash-dot broken lines in the drawings illustrate the display screen while the even broken lines illustrate portions of the graphical user interface. No subject matter shown in either broken line styles form part of the claimed design. 

CLAIM The ornamental design for the display screen or portion thereof with a graphical user interface, as shown and described. 